Electric coil



April 14, 1942. c, NIEMANN 2,279,581

ELECTRIC COIL Filed July 1, 1958 INVENTOR. CawljViczma/z/z Patented Apr. 14, 1942 ELECTRIC COIL 4 Carl N-iemann, Erlangen, Germany, assignor to the firm Siemens-Reiniger-Werke Aktiengesellschaft, Berlin,- Germany Application July 1, 1938, Serial No. 216,979

, In Germany July 3, 1937 2 Claims.

This invention relates to electric coils, and is particularly concerned with a new high tension coil for transformers of small dimensions adapted to carry high voltages and small currents, especially-such as are used in Roentgen apparatus.

The requirement for reducing the dimensions of such transformers as much as possible introduces numerous problems in the choice and arrangement of parts, particularly with respect to providing for adequate insulation. It is comparatively easy to insulate the coil against the iron core and against the grounded transformer housing, for example, by means of paper bandages; however, considerable difliculties are encountered in insulating the individual windings or coil layers, which have to carry relatively high voltages, against one another in such a manner that a breakdown from the outermost to the innermost layer is prevented. The reason for these difflculties' may be found in the fact that, although the insulating medium, such as paper inserted between the coil layers, provides relatively good insulation against transverse loads, creepage may occur along the interior surface of the paper bandage from the outer to the inner coil layer, and such creepage may eventually'result in a breakdown along the path over which it takes place.

The object of the present invention is to furnish a coil which avoids the above noted draw- :r

backs. This is accomplished by extending the cylindrical insulating layers disposed between the I individual coil layers beyond both ends of the coil, and cutting or tearing portions of the insulation which overlie the ends of the winding of ,-y

the coil at intervals so as to produce wings or strips which are then folded back over the ends of the coil in such a manner that the creepage paths are lengthened to such an extent that a breakdown from the outer to the inner coil layer high tension coil has the desired number of layers, illustrated for the sake of convenience by eight layers 28 to 35. Numerals 36-43, inclusive, indicate the insulating sheets provided between these layers. Additional cylindrical insulating members 20 and 2| are disposed on the inside and on the outside of the winding, as shown. The end portions of the insulating members or sheets 36-43 extend beyond and overlie the ends of the winding. They are non-uniform in length and are cut or torn at approximately equally spaced points, and the strips or wings which are thus formed are folded back over the ends of the coil or winding and over the insulating members 26 and 2|, as shown. Inasmuch as the center of the Winding is grounded, the wings of the insulating members 36 to 39, inclusive, are folded toward and over the central insulating member 26 of the coil, while the wings of the insulating members 40 to 43, inclusive, are folded toward and over the outside insulating member 2|, The folded wings of theinsulating layers are interlaced or telescoped into each other, at the inside as well as the outside of the coil, to maintain the cylindrical shape of the coil. The creepage path -K is extraordinarily long due to the interlacing and overlapping of the wings or end strips of the insulating sheets and extends labyrinthlike between the interlaced wings. The structure may be provided with an additional insulating bandage I2 which, however, is not absolutely necessary, because the folded ends 36-39 of the insulating sheets will in most cases provide sufficient insulation against the iron core.

The end view, Fig. 2, indicates the arrangement of the individual wings or strips 4% (full line) and 45 (dotted line) of two successive insulating layers. A number of the wingsor strips which are folded back upon the outside or the coil winding are indicated in position before completing the folding, while others are shown folded in place. Care is taken that the wings such as 44 of layer 40 overlie the spaces between the wings 45 of layer 41. This must be considered in cutting or tearing the extending end portions of the insulating sheets which are to form these wings. Generally speaking, it will suffice to cut or tear the extending end portion ofthe insulatinglayers at approximately equal intervals. The arrangement of the wings or strips such as 36-39 (Fig. 1) which fold inwardly upon the inside of the coil Winding is similar. Inasmuch as the diameter of the winding, and with it the circumference, increases from the inside to the outside, the spaces between the wings will not be in alignment in the successive layers.

The folded wings or strips of the insulating layers may be glued or secured in place by means of paper tape or the like. The dielectric property of the layers may be increased by immersion oi. the coil in oil or other suitable insulating medium. 1

What is desired to have protected by Letters Patent of the United States is specifically defined in the appended claims.

Iclaim:

1. In a transformer, a high tension coil winding comprising a plurality of layers, each layer comprising a plurality of turns, sheets of insulating material disposed between said layers and projecting at the ends of the winding, each sheet having a long projecting portion at one end of the winding and a shorter projecting portion at the other end and the sheets being arranged with the long projecting portions of each. sheet alternating with the short projecting portions of adjacent sheets at each end of the winding, said projecting portions being divided axially of the winding to form separate wings, the lines of division' being angularly displaced in successive sheets, the wings of a plurality of said sheets being folded outwardly around the ends or the inside layer until they substantially meet, the

junctions between the ends of the wings of each sheet as well as the axial divisions between such wings being covered by the wings of an adjacent sheet, and means for securing said wings in -folded position.

2. A coil winding as claimed in claim 1, wherein 'two sheets of insulating material are providedbetween two of the layers of the winding which are approximately midway between the outside and inside layers, the wings of one of said sheets being folded outwardly and the wings of the other sheet being folded inwardly.

CARL NIEMANN. 

